Electrical machines usually comprise a housing-fixed stator as well as a rotor which can be moved relative to the stator. The rotor may be supported so as to be rotatable with respect to the stator or so as to be linearly movable relative thereto, for instance. Electrical machines are classified as electro-mechanical energy converters. In that context, they may operate as a motor or generator.
Electrical machines may be used for the propelling system in motor vehicles, for instance. To this end as well as for other applications, it may be of advantage to achieve defined characteristics of the operational behavior of the electrical machine. The torque, the acoustic properties, the iron losses as well as the losses in the windings and in the magnets may be among these characteristics.
A stator of an electrical machine with concentrated windings is distinguished by a compact design compared to those with distributed windings. Here, different pole pair numbers may be combined with differing numbers of slots in the stator. The number of the pole pairs in the rotor is understood to be the pole pair number. The slots in the stator serve to receive the windings. Each magnetic pole pair in the rotor normally comprises two magnetic poles, a north pole and a south pole.
Document US 2007/0194650 A1, for instance, describes an electrical machine comprising twelve slots and ten poles. In a machine of this type, the magnetomotive force MMK induced in operation by the stator is not distributed according to a simple sine wave. Rather, it is obvious when analyzing the magnetomotive force and its harmonic components, for instance by means of a Fourier decomposition, that numerous undesired harmonic components occur. Here, all harmonic components other than the one used as the operating wave of the electrical machine are undesired as these may result in losses and, in addition, may cause undesired acoustic impairments.
It is not necessarily the main wave which is applied as the operating wave in machines with concentrated windings. It may rather be of advantage to use a higher-order harmonic component of the magnetomotive force as the operating wave.
To give an example, the fifth or seventh harmonic component may be used as the operating wave in an electrical machine comprising a stator with concentrated windings, two adjacent teeth being provided with coils of a strand (sometimes also referred to as “phase”) and in the opposite winding sense. In the basic form, this results in a machine with twelve slots and ten poles or with twelve slots and 14 poles. Integer multiples of the number of the slots and of the number of the poles are also possible here.